Vapor-electric device



Nov. 25, 1952 w. E. PAKALA 2,619,

VAPOR-ELECTRIC DEVICE Filed March 9, 1949 2 SHEETS-SHEET 1 Fig.2.

WITNESSES: INVENTOR William E. Pokolcl.

ATTORN EY Nov. 25, 1952 w. E. PAKALA 2,619,617

VAPOR-ELECTRIC DEVICE Filed March 9, 1949 2 SHEETS-SHEET 2 WITNESSES: v INVENTOR 35 William E. Pukolo.

BYJ/JW ATTORNEY Patented Nov. 25, 1952 VAPOR-ELECTRIC DEVICE William E. Pakala, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 9, 1949, Serial No. 80,402

My invention relates to a vapor-electric device,

and particularly to a method and apparatus for reducing the probability of electric valve.- p

, The most serious difiiculty encountered in the arc-back in a vapor- I potentials and currents existing in the modifi- 4 Claims. (01. 315-111) LEI operation of vapor-electric valves is the tendency 1 of such valves to are back at random'times. Experiments have indicated that these arc-backs are probably the results of so-called arc-back causes established at the surface of the anode; and while these arc-back causes are not exactly known, they are believed to be the result of contamination of the surface of the anode. Experiments have indicated that these arc-back causes may be burnt off or eliminated when an inverse discharge is established to the anode for a period of the orderof five microseconds-or rather between three and ten microseconds and do not reappear. In a series of five hundred experiments, only one arc-back cause was found to exist after an inverse discharge lasting approximately five microseconds.

According to my invention, I provide apparatus for causing inverse negative pips or discharges having a time of the order of five microseconds during each of the scheduled non-conducting intervals of the valve. Preferably, these negative pips occur either at the beginning or the end of the non-conducting interval although apparently they will be effective regardless of the time during the interval at which they are applied. In the apparatus according to my invention, a capacitor is connected across the anode and cathode of the electric valve, and this capacitor is charged to a potential substantially twice the normal inverse potential appearing between the anode and cathode; that is, the potential appearing during the normal non-conducting period of the valve. A grid control valve is placed in series with the anode and cathode of the valve, and, the capacitor to control the time of discharge of the capacitor, through the vaporelectric valve.

It is, accordingly, an object of my invention to provide a method of reducing the probabilities of arc-back in a vapor-electric valve.

It is a further object of my invention to provide apparatus for producing negative pips in a vaporelectric valve.

It is a further object of my invention to provide a system forapplying timed negative discharges in a vapor-electric valve.

Other objects and advantages of my invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 7

Figure 1 is a schematic illustration of a preferred embodiment of my invention;

Figure 2 is a diagrammatic illustration of the currents and voltages involved in the apparatus in Figure 1;

Figure 3 is a modification showing independent timing of the negative pips; and

Figure 4 is a diagrammatic illustration of the cation according to Figure 3.

In an exemplary embodiment of my invention according to Figure 1, an alternating-current circuit I0 is connected to a direct-currentcircuit l I by means of a rectifier transformer I2, and the flow of current between the circuits H and I0 is controlled by means of vapor-electric valves [3 connected to the terminals l to 6 of the rectifier transformer [2.

For simplicity of illustration, only two of the vapor-electric valves I3 are illustrated, but it is apparent that valves l3 will be attached to all of the valve terminals l to 6 of the transformer l2. In the illustrated embodiment of vapor electric valves, each valve l3 comprises a container [4 having therein a main anode 15, a vaporizable, reconstructing cathode l6 and a make-alive electrode ll. Associated with the make-alive electrodes is an impulsing system [8 preferably of the so-called saturable reactor type.

Connected in shunt with each of the vaporelectric valves I3 is a capacitor 20 having in series therewith a grid control valve 2| by which the potential of the capacitor 20 may be discharged between the anode I5 and cathode l6 of the vapor-electric valve [3. Preferably, a blocking capacitor 22 is installed in series circuit relation between the control capacitor 20 and the anode and cathode circuit to produce a definite termination of current flow in the protective circuit. Usually a discharge resistor 23 is connected to dissipate the charge received by the blocking capacitor 22.

Preferably, the control capacitor 20 is charged to a potential 24 substantially double the normal potential 25 appearing between the anode I5 and cathode l6 during the inverse or non-conducting interval. The potential 24 may most readily be supplied from a periodic source herein indicated as a polyphase transformer 26 supplied from the alternating-current circuit Ill. Usually charging impedances 21 are placed between the terminals of the periodic source of potential 26 and. the capacitors 20 to control the rate of charge of the capacitors 20.

In the preferred embodiment, the discharge of the control capacitor 20 is established by means of a transformer 30 associated with the anode conductor so that the decay or termination of the normal anode current 3| will produce a potential 32 which will render the grid of the grid control valve 2| positive and permit the discharge of the capacitor 20 in an inverse direction between the anode l5 and cathode Hiof the vapor-electric device I3. If necessary to control the timing, a biasing potential 33 may be inserted between the current-controlled transformer 30 and the grid of the grid control valve 2 I. V

In the operation of a protective system according to Figure 2, the periodic control potential M will be applied to the control capacitor 2%] charging up the capacitor 20 to a potential substantially twice the normal inverse potential 25 of the valve 53. At the termination of the normal anode current Si, the decay of the anode current will produce a voltage pip 32 in the control transformer 38 which will overcome the bias 33 and trip the grid of the grid control valve 2! permitting the discharge of the capacitor 28 to produce a high-current impulse SEof very short duration usually of the order of three to five microseconds. In operation, this discharge 35 burns off or dissipates the backfire causes and then is itself extinguished before arr inverse current can be established in the power circuits feeding the vaporelectric valves l3. 7 In other words, the brief negative impulse is applied during the normally nonconducting period of the main power-circuit, preferably near the beginning or enclof said normally non-conducting power-circuit period,- 5712.

that is, at a time when the inverse voltage of the main power-circuit is near zero, or low enough not to sustain the are formed by the brief negative impulse, the duration of the normally non-conducting power-circuit period being much longer than the impulse-period. Usually, the normal inductance of the anodeleads and the transformer windings is such that no inverse current can start in a period less than ten microseccnds. transformer l2 should for some reason be utilized, the time interval could readily belengthened by providing a reactor (not shown) in the anode circuit. i

In the modification according to Figure 3, the firing circuit has been made totally independent of the anode current so that if. desired the, negative pips 35 may be established at any time interval suchasthe termination of thenore mal inverse period. While it is notknown when or how the backfire. causes are established, it is believed that they are established during. a normal non-ionized and. non-conducting interval in the valve. is. Consequently,,it may be desirable in some instances to havethe ne ative pips 35 preceding the normal conducting interval. This may be particularly true in inverters I,

The controljor thegrids of the valves 21 is provided by an auxiliary winding at on the transformer 26 and instead ofimpulses 32 the firing potential may be of substantially sine wave form as shown at 4|.

1n tl'i'eo'peration of this modification, the phase is adjusted so that the. discharg of the capacitor 20 occurs at any desired point in the none conducting interval and preferably near the end of the non-conducting interval. The inversedischarge then burns off or. dissipates any are back causes that may have accumulated during the preceding cycle. e e

For the purpose of illustration, I have shown and described exemplary embodiments of my invention and described the same to the best of my present knowledge, but it will be apparent that changes and modifications can be made therein without departing from the true spirit of my invention or the scope of the appended claims.

I claim as my invention:

1. A d e-contamination system for a vapor-elec- However, in the event 'a low-impedance tric valve having a main anode, and cathode subject to an alternating potential and having alternate conducting and normally non-conducting periods with inverse potential between said cathode and anode during said non-conducting period comprising a source of auxiliary potential, circuit means including a grid-controlled electric valve applying said auxiliary potential inversely between said anode and cathode an i grid control means for periodically energizing said grid-controlled electric valve to produce a short time discharge of said auxiliary source inversely between said cathode and anode during the normally non-conducting period.

2. In a vapor-electric device having a main anode a'nd cathode subjeetto alternatni'g poten tials, an arc-back restraining systeincomprising a source of potential having a value in excess'o-f the normal back voltage impressed pntheafiode. and an electric valve connected to impress the potential of saidsource in the reverse direction between said cathode and anode for an interval of the order of five microseconds during a norr'rially non-conducting interval in saidgvalve.

3. A de-c'ontamination system for a vapor-'eelec trio valve having amain power-circuit including a' main anode and cathode subject to a powercircuit alternating" potential and having alter sate conducting andnormally Iron-conducting periods with inverse potentiar between said oath ode and anode dui'ingsaid non-conducting period, comprising a source of auxiliary potential, circuit means including a gri'd co'ntrolled electric valve for applying said auxiliary potentialfin-- versely between said anode and cathode, arid grid control means for periodically energizing said grid-controlled electric valve to produce a short time discharge of said auxiliary source inversely between said cathode and anode during the nor:- mally non-conducting power-circuit period at a time in said power-circuit period when the inverse power cir'cuitvoltag'e is near zero; the duration of said normally non-conducting power-circuit period being much longer man the duration of said short-time discharge.

4. In a vapor-electric device having a i'riain" power-circuit including a main anode and cathode subject to alternating main-circuit potehnais'; an arc-back. restraining system comprising a source. of potential having a value in excess of the normal main-circuit back-voltage impressed onv theanode, and an. electric valve connected to impress the potential of said source in the reverse direction betweensaid cathode and anode for an impulse-interval of. the order of five microseconds, during a normally non-ccnducting power-circuit interval in said valve at a time in said powerecircuit interval when the normal main-circuit ,backevolt'age. is; low, the duration of said normallyhonz-conducting vpou rercircuit interval being much longer than: the impulseinterval. 7 Q. l

WILLIAM ErPAKA'LA REFERENCES CITED The following referencesareof re'i'zo'i'd in the file of this patent:

UNITED STATES PATENTS Number Name 7 Date 1,691,395 Langmuir" Nov. 13., 1928 2,147,472 Ulrey Feb; 114, 1939 2,202,720 Spielhagen May 28; 1940 2,221,569 Berkey Nov; 12; 1940 

